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I want to do something a little more complicated than un-submodule a git submodule

I have a top-level git repo that contains submodule repos.

I want to perform a filter-branch history rewrite on the top-level repo, and essentially incorporate the files from the corresponding submodule version at each commit in the top-level history.

This can also be described as the reverse of Convert a git folder to a submodule retrospectively?

For example,

Submodule repo has history 

A--B--C--D

Top repo has history 

X--Y--Z where X[points to A]--Y[points to B]--Z[points to D]

The naive solution described in the other question would result in:

A--B--C--D \ > M / X--Y--Z

I would like instead:

X'--Y'--Z' where: X' is X plus the files from A Y' is Y plus the files from B Z' is Z plus the files from D'

Addressing comment from user torek: Note that commit C is lost, and commit D' contains all the changes from commits C and D. This is not by choice, but a simplification. I would also be just as happy with a commit C' (the changes from C) just showing up between Y' and Z', unfortunately that introduces other edge cases that are not worth solving for.

What have I tried so far?

Spent some time trying to articulate what I want to do and researching existing SO questions.

Is this an XY problem?

No, it's not. This is not part of some larger problem that I'm actually trying to solve.

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  • Worth noting: if the superproject has, say, 3 unique gitlinks to the submodule, but the submodule itself has more than 3 commits, you will almost certainly omit all but three of the submodule commits in the rewritten, de-submodule-ized superproject. If you wish to avoid that you have a much harder problem as there's no guarantee that the superproject commit graph and submodule commit graph are conformable. Commented Sep 21, 2019 at 18:41
  • Yes, good catch. I updated the question to show a lost commit from the submodule repo. Commented Sep 21, 2019 at 18:44

1 Answer 1

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A submodule is a (perfectly ordinary) repository, if you want to read stuff out of its commits you can add its object db to your search.

GIT_ALTERNATE_OBJECT_DIRECTORIES=$PWD/.git/modules/mysubmodule/objects \ git filter-branch --index-filter ' if subcommit=`git rev-parse -q --verify :path/to/submodule`; then git update-index --force-remove path/to/submodule git read-tree --prefix=path/to/submodule/ $subcommit fi ' -- --all GIT_ALTERNATE_OBJECT_DIRECTORIES=$PWD/.git/modules/mysubmodule/objects \ git repack -ad

should do it.

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7 Comments

The git rev-parse seems to be failing when executed inside the filter. There is no error message, just a non-zero exit code :-(
Removing the -q option I get... fatal: Needed a single revision tree filter failed: git rev-parse --verify :*** where *** is my submodule path. When I change it back to an index-filter the error is the same
Fixed its behavior when path/to/submodule doesn't exist, sorry for oops. but where are you getting a tree filter from? this is an index filter. Ah, I see you were just trying it.
Yeah sorry I changed the index-filter to a tree-filter while debugging. It's back to an index-filter now.
Failed halfway on failed to unpack tree object... I think there was a deleted commit at some point the submodule's history
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